For instance, metal plating process has been heretofore conducted in the stages (1) to (4) in sequence:
(1) A stage of removing smears or extraneous matter such as oil attached to the surface of an article to be plated (Pre-treatment Stage); PA0 (2) A stage of immersing the article thus cleaned into a plating bath to plate it (Plating Treatment Stage); PA0 (3) A stage of lifting and withdrawing the resulting plated article out of the plating bath and washing it with water (Water-washing Treatment Stage); and PA0 (4) A stage of draining or dewatering and drying the plated article thus washed (Drying Stage).
In the stages (1) to (4) above, the pre-treatment stage (1) must be performed so that the extraneous matter on the article for plating may be completely removed without impairing the article. The drying stage (4) must be performed in such a manner that the water content may be dried homogeneously and sufficiently. Such non-uniform drying that non-uniform wet portions or water droplets are left behind on the article should be avoided as far as possible. This is because when the non-uniform wet portions or water droplets are spontaneously evaporated after the drying stage, these adsorb dirt and dust in the air, so that after the spontaneous evaporation spot-like dirt and water deposits are left behind.
Accordingly, in order to conduct washing and drying while fulfilling the above-mentioned conditions, a wash and dry apparatus in which an organic solvent is used instead of water has been adopted. A conventional wash and dry apparatus in which an organic solvent is used will be explained with reference to FIG. 1.
In FIG. 1, a working bath 1 is partitioned, at its bottom and lower zone, into a draining bath 1a, a first washing bath 1b, a second washing bath 1c and a wash and dry bath 1d. The draining bath 1a contains an organic solvent solution 2 mixed with a surfactant, and the washing baths 1b, 1c and the wash and dry bath 1d contain each an organic solvent 3 free from any additive. A pipe (not shown) is provided so that the organic solvent solution 2 flowed into the draining bath 1a may flow from the bath near the liquid level outwardly. A further pipe is provided so that the organic solvent 3 may flow through the washing bath 1c via the pipe from the washing bath 1b into the wash and dry bath 1d. The organic solvent 3 flowed out of the wash and dry bath 1d is purified for recycling.
At the bottom of each of the baths 1a, 1b, 1d, a heater 4 is positioned. These heaters serve to heat the organic solvent solution 2 and the organic solvent 3 to generate gas or vapor 5 of the organic solvent, which fills the chamber inside the working bath 1.
Along the inner side wall of the working bath 1, a cooling pipe 6 is disposed in a coiling manner, and cooling water or cooling gas such as Freon is routed through the cooling pipe. Below the cooling pipe 6, there is provided a gutter 7 for recovering the solvent. The organic solvent gas 5 is condensed upon contact with the cooling pipe 6 to produce liquid droplets which flow down into the solvent recovery gutter 7 and are returned to the washing bath 1c. In this way, loss of the organic solvent gas 5 out of the upper opening of the working bath 1 is minimized.
The organic solvent to be used includes for example, trichloroethylene, 1,1,1-trichloroethane, methylene chloride, trichlorofluoroethane, etc.
A sequential process of draining and drying the plated article which was preliminarily washed in water by means of the apparatus of FIG. 1 is performed in the following steps (I) to (IV):
(I) The plated article 8 having water droplets deposited thereon is immersed into the organic solvent solution 2 within the draining bath 1a, whereby the water droplets are separated from the plated article by the action of the surface active agent and floated on the liquid level. These water droplets are removed out of the bath along with the organic solvent solution 2. Then, the plated article is lifted and withdrawn from the organic solvent solution 2, drained and dried. Thus, the plated article free from water droplets is obtained.
However, the surface active agent remains attached to the surface of the plated article thus dried and will be removed in the subsequent washing stage which will be explained below.
(II) The plated article after draining is immersed in the organic solvent 3 within the washing bath 1b for a while and withdrawn. During immersing, the organic solvent 3 within the washing bath 1b is heated to elevated temperatures with the aid of the heater 4, and the surface active agent deposited on the plated article is readily dissolved into it and substantially washed out.
(III) Then, the plated article withdrawn from the washing bath 1b is immersed into the next organic solvent 3 within the washing bath 1c. Into the washing bath 1c is flowed the purified organic solvent 3 from the solvent recovery gutter 7. The plated article is washed with the organic solvent 3 within the bath 1c and concurrently, is cooled below the boiling point of the organic solvent. This is because a cooling pipe (not shown) is disposed in the washing bath 1c, in which the organic solvent 3 is preliminarily cooled.
(IV) After cooling in the washing bath 1c, the plated article 8 lifted and withdrawn from it and is, as shown in FIG. 1 in phantom line, stopped and suspended above the liquid level of the organic solvent 3 in the wash and dry bath 1d for a while to be exposed to the organic solvent gas 5 which is at elevated temperatures. The organic solvent gas 5 is condensed on the surface of the plated article which is cooled to produce liquid droplets, and the droplets flow down continuously along the surface of the plated article and drip. In this way, by dripping of the droplets the plated article can be thoroughly washed.
When the plated article reaches gradually the same temperature as the boiling point of the organic solvent, the organic solvent gas 5 is no longer condensed on the surface of the plated article, so that it becomes dry. At this stage of condition, the plated article is lifted upwardly and withdrawn out of the working bath 1.
By a series of the operations above, draining, cleaning and drying of the plated article are thus finished.
In case where a pre-treatment step for removing smears or extraneous matter such as oil attached to the plated article is conducted, the step (I) above is omitted and the step (II) is then the first step. The extraneous matter or smears such as oil can be likewise removed as in the case of surface active agent as described above.
The present inventors, however, have found that the foregoing conventional apparatus has difficulties or defects which will be described below.
That is, the leakage of the organic solvent gas 5 from the upper opening of the working bath 1 can be diminished to a certain degree by condensing and recovering it by the provision of the cooling pipe 6 and recovery gutter 7, but the leak-tight effect is not still satisfactory. Substantial loss of the solvent still occurs, which is not economical and dangerous in that the leaked organic solvent gas 5 may be hazardous to the health of workers.
It is conceivable that this drawback can be eliminated by making the height of the working bath 1 larger or lowering the temperature of the cooling tube 6 thereby to increase the recovery efficiency, but these solutions pose new problems. In case of the former, the work of immersing the plated article 8 and being immersed consecutively into the respective baths will be difficult. In case of the latter, the temperature within the working bath 1 becomes unnecessarily low and as a result, the plated article is too cool in the course of lifting it up above the bath 1d, so that immediately when it is withdrawn out of the working bath water vapor in the air will be unsuitably condensed on the cold, plated article. For this reason, in actual practice, the temperature of the cooling pipe 6 can be merely set at the utmost in a range of from 10.degree. to 15.degree. C.
In view of the present state of the art, the present invention has for a primary object to provide a washing apparatus with which leakage of the gas of washing liquid can be decreased to a substantial degree while retaining good working efficiency and washing effect.